NGO: Revealing a Hidden Universe Bernard Schutz AEI, Potsdam, Germany & Cardiff University, Wales

NGO: Revealing a Hidden Universe

Bernard Schutz

AEI, Potsdam, Germany&

Cardiff University, Wales

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B F Schutz NGO 02 April 2012

NGO: First GW Observatory in Space LIGO, VIRGO likely to make first detections 2015-17.

– Primary sources: neutron star and stellar black hole binaries, ~50/yr.– Limited: low SNR (< 20), stellar-mass sources, f > 10 Hz.

Pulsar timing could open nHz band before 2020.– Signal confusion, limited information: 3 cycles/10 yr.

GW detection in space opens the richest GW band: mHz.

1. High SNR (~103), thousands of resolvable signals.

2. Astronomy’s focus is moving toward NGO’s capabilities: – Massive galactic black holes, key also to galaxy evolution.– Transient astronomy: major ground-based facilities coming.– The high-redshift universe: astronomy's next frontier.

3. Large community of astronomers now exploring science outcomes of space-based GW detection for many branches of astronomy. More than 2000 papers on ADS!

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NGO offers revolutionary science

Massive BHs (105--107 Mo) Measurement of mass at z = 1 to ±0.1%, spin a/M to ±0.01. Mass function, central cluster of black holes in ordinary galaxies to z = 0.5.

Evolution of the Cosmic Web at high redshift Observation of objects before re-ionisation: BH mergers at z >> 10. Testing models of how massive BHs formed and evolved from seeds.

Compact WD binaries in the Galaxy Catalogue ~2000 new white-dwarf binary systems in the Galaxy. Precise masses & distances for dozens of systems + all short-period NS-BHs.

Fundamental physics and testing GR Ultra-strong GR: Prove horizon exists; test no-hair theorem, cosmic

censorship; search for scalar gravitational fields, other GR breakdowns. Fundamental physics: look for cosmic GW background, test the order of the

electroweak phase transition, search for cosmic strings. Europe can take ownership of this new science: only Europe has the

technical expertise to put a mHz GW observatory into space!

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NGO: Sensing Spacetime Vibrations

Generated by motions of mass and energy. Required by special relativity; details test GR. When we detect waves we are directly

sensing a part of the gravitational field of a very distant system.

Wave is a record of the motion of distant matter: phase of wave encodes information.

Gravity (including waves) – penetrates any matter;– reaches us from the black holes event horizon;– reaches us from the end of inflation.

Gravitational Waves carry entirely new information

about the Universe!

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Weak waves carry huge energies

Coupling of GWs to matter is very weak, h << φ/c2 = GM/rc2 – This leads to δL/L ~ h ~ 10-21 to 10-24 (amplitude of wave).– Negligible scatter, absorption: almost perfect messengers (modulo lensing)!

Waves carry huge energy flux; luminosity scale is c5/G ~ 3.6 × 1059 erg/s. BH mergers reach 1% of this.– Why? Spacetime very stiff: small deformation h requires huge energy.

(AEI)

Black hole mergers are more luminous than the rest of the universe put

together!

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Like listening to the universe

GW detection analogous to listening to sound: spacetime waves

Detectors are our “microphones”– 1D response, not an image. Converts to sound: you can listen to GWs,

pack them in an MP3 file.– Waves are recorded coherently, tracking phase and amplitude.– Detectors are nearly omni-directional, but linearly polarised.

(AEI/Milde Science Comm/getye1/Novak/Willmann)

Ideal monitor for transients!

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NGO Heliocentric Orbit

(Milde Science Communications, Exozet)

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NGO: Principles of Operation

Transpondinginterferometry

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Free-fallingproof masses

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S/C an isolationshield (μN jets)


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S/C an isolationshield (μN jets)

Science data rate low: ~100 bps


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NGO Technology Links between S/C 106 km apart

– Laser power needed: ~ 2 W. – Precision : ~ 10 pm/sqrt(Hz), ~100 x better than Michelson-Morley!

All technologies inherit from LISA – LISA had several industrial studies in US and Europe, most recently

Astrium's Formulation Phase Study that began in 2005 and ended on Dec 16, 2010 with the Mission Consolidation Review.

Isolation and fringe measurement technologies will fly on LISA Pathfinder (LPF) 2014.

- Carries optical bench, lasers, 2 proof masses, thrusters.

- Test-mass separation ~ 0.5 m, no sensitivity to GWs.

- Gravitational Reference Sensor (GRS) is European.

LPF is a complete test of 1 NGO arm, apart from SC-SC link.

LPF systems designed to meet NGO requirements.

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NGO’s Ground Testing

Torsion pendulum test of isolationcontrol – red measurements are all upper limits: need to go into

space to do better!

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LPF: The Technology of Stillness

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LPF Optical Assembly

The LPF Flight Model is completely integrated, has undergone environmental testing, waiting integration of clamp assembly and micropropulsion.

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Retiring risk with LPF

The most important lessons for building NGO have already been learned by building LPF! – Key lesson: developing European skill base, distribution of work.– LPF/NGO partners: Italy (LPF PI), Germany (NGO lead), France, UK,

Spain, Switzerland, Denmark.

LPF is an “engineering model” for NGO in space, because we cannot duplicate flight conditions on ground. – Ground testing already shows that performance will be close to spec.– LPF richly instrumented to monitor performance of every system and

subsystem.– If LPF shows up problems, there is time to incorporate the lessons into

NGO.

LPF expected performance is better than needed for good NGO science.

Retiring risk with LPFDeveloping Expertise

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NGO Mother S/C Payload, Instrument

Daughter payload identical (but just one per S/C).

(from LPF)

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NGO S/C

All 3 S/C buses, propulsion modules are identical.

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Sensitivity and BH Science of NGO

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106 M๏ @ z=1, SNR=1640

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106 M๏ @ z=1, SNR=1640

105 M๏ @ z=20, SNR=49

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106 M๏ @ z=1, SNR=1640

105 M๏ @ z=20, SNR=49

104 M๏ @ z=5, SNR=15

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106 M๏ @ z=1, SNR=1640

105 M๏ @ z=20, SNR=49

104 M๏ @ z=5, SNR=15

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106 M๏ @ z=1, SNR=1640

105 M๏ @ z=20, SNR=49

104 M๏ @ z=5, SNR=15Unresolved binary

systems

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106 M๏ @ z=1, SNR=1640

105 M๏ @ z=20, SNR=49

104 M๏ @ z=5, SNR=15

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Up close to BH mergers

NGO should detect 10-200 BH-BH binary mergers in 2 years.

Listen!

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Up close to BH mergers

NGO should detect 10-200 BH-BH binary mergers in 2 years.

Listen!

Direct measurement: masses to ±0.5%, spin magnitudes to ±0.01.

Spin alignments: wet or dry merger.

No complex modeling needed: these data are directly encoded in phase of inspiral waveform.

Test GR in strong gravity at the edge of a black hole. Compare merger in detail with numerical simulations in GR (and if

needed, in other theories). Look for violations of cosmic censorship: still a conjecture in GR! Look for evidence of other gravitational degrees of freedom; test

energy and angular momentum balance (before and after).

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Up close to BH mergers Detailed comparison with numerical relativity simulations

will reveal mass & spin of final merged BH, test GR.

Numerical relativitysimulation by AEI; viz by M Koppitz, Milde Science Comms, Exozet Babelsberg

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Observing the entire universe

NGO will detect ALL the mergers in the universe in its frequency band, even out to z=15 and beyond if they are happening.

(At z=15, T = 2.7 x 108 yr.)

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How did SMBHs form and grow? NGO will detect enough mergers to z = 15 to discriminate

among different seed models (early or late), accretion models, metallicities.

M. Volonteri: “Most if not allmassive black holes are in

the LISA band at some pointin their cosmic evolution.”

(Volonteri 2010)

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Discriminating models of MBH growth Simulated example: NGO can determine model parameters

even for high-z BH evolution.

Consider a “hybrid” seed model: fraction F of BHs originates from small early seeds (Pop III BHs) and the remaining fraction (1-F ) originates from later large seeds (more recent gas cloud collapse).

True valueused in the simulation.

(Sesana et al 2012)

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Extreme Mass-Ratio Inspirals: EMRIs

Stellar-mass BH capture by a massive BH: dozens per year to z~0.7.

We have measured the mass of the GC BH using a few stars and with at most 1 orbit each, still far from horizon.

Imagine the accuracy when we have 105 orbits very close to horizon! GRACE/GOCE for massive BHs.

– Prove horizon exists.

– Test the no-hair theorem to 1%.

– Measure masses of holes to 0.1%, spin of central BH to 0.001.

– Population studies of central and cluster BHs.

– Find IMBHs: captures of 103 Mo BHs.

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(EMRI movie)

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Compact binaries NGO will make major contributions to the study of binary

evolution and the endpoint of stellar evolution.

1. The mission has guaranteed (known) sources: verification binaries

Known binariesand strongest1000simulatedbinaries

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Compact binary astrophysics

Synergy with GAIA, upcoming large-area surveys, radio pulsar binary surveys

NGO supplies unique new information:– Orbital inclination (helps determine masses)– Accurate distance (for known masses, or for chirping systems)– Discovery of distant/obscured/faint binaries.

These observations address key astrophysics issues, e.g.:– Binary evolution, common envelope evolution

– Precursors of Type Ia supernovae in the Galaxy

– Population studies of Galaxy, tracers of star formation

– Interacting binaries, mass transfer, tides

– Population studies of NS-NS, NS-BH, BH-BH binaries

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Handling NGO’s data

Data volume tiny, but extensive analysis required to:– separate overlapping signals;– precisely measure parameters of loud BH events;– dig EMRI events out of instrumental noise.

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MLDC – Mock LISA Data Challenge – has essentially solved these problems.

- MCMC, MultiNest, other algorithms have proved effective.

MLDC generates realistic, synthetic data sets.

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Symmetry breaking after Big Bang

pulsars LIGO

aLIGO

NGO

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Unique Science, European Science

As the first instrument able to listen to gravitational disturbances from all over the universe, NGO will uncover information obtainable in no other way, impacting physics, astronomy, & cosmology.

NGO targets the twin Cosmic Vision goals of exploring fundamental physics and understanding the early universe: deviations from GR, physics of inflation and symmetry breaking, weaving the cosmic web, origin of massive black holes, endpoints of stellar evolution. The mHz frequency window is especially rich in strong GW sources that inform all these issues.

Because we have built LISA Pathfinder, ONLY Europe can do NGO. Without Europe, this rich mHz GW science will not be done until after 2030-35.

With NGO, Europe will dominate GW astronomy the way CERN dominates high-energy physics. This really is a Cosmic Vision!

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After L1: LISA or NGO At this point, resources available for next opportunity are not

known: mission could be LISA, NGO, or somewhere between.

Cost savings for NGO: weight costs fuel costs money– Shorter arms (1 Gm) save fuel, reduce sensitivity.

– 2 Gm would not cost much more.

– Drift-away orbit saves fuel, limits lifetime.– Another fuel-saver would be a lunar fly-by assist.

– Dropped third arm, saved weight of experiment packages, loses pol’n.– Marginal saving, would not take much extra resource to restore.

– Highest science priority: next proposal should have 3 arms!!

Total budget of NGO (including member states) ~90% of full LISA mission if it were done by Europe. – Lesson 1: Descoping loss more science than it saves money.– Lesson 2: Collaborating brings in more resources but also raises the

total cost.

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Next: There were many reasons to be dissatisfied with ESA’s

process for the L1 selection.

BUT: my guess is primary reason NGO was not selected was fear of unknown risk: LPF has not yet flown, and GP-B has shown that ultra-high sensitivity experiments in space are difficult.

Conclusion: LPF is key. Once LPF flies successfully, this fear will be reduced.

Strategy: we must make sure LPF is understood and admired in the European space science community. – GP-B did a very good job of telling its story before launch: smoothest

spheres ever constructed, tiniest effects of GR, etc. – We need to get the LPF message out: creating quietest place in solar

system, measuring tiny external forces on S/C, balancing internal gravity.

– LPF test of MOND would be very helpful for next LISA competition!

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EMRI Parameter Errors (MCMC)

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MBH Merger Distance Errors (MCMC)

Documents

NGO: Revealing a Hidden Universe Bernard Schutz AEI, Potsdam, Germany & Cardiff University, Wales